Ben's physical appearance has changed throughout the series from a ten-year-old to a sixteen-year-old.
However, he retains some recurring characteristics. He has shaggy brown hair, green eyes, pale skin, and he's quite skinny for his age, though he shows a lot of muscle definition due to being athletic.
He wears brown cargo pants with pockets at the knees and green and white shoes.
Benjamin Kirby "Ben" Tennyson was a normal ten-year-old kid until he found the Omnitrix, a powerful watch-like device that allowed him to turn into ten different aliens.
Though initially immature and clumsy, Ben grew to be a true hero.
Ben wore the prototype Omnitrix in Alien Force and the Ultimatrix in Ultimate Alien on his left wrist.
In Omniverse, Ben wears a black shirt that has a green stripe in the middle with a white 10 and green stripes on the sides of his shirt.
He is also a crafty fighter and actually uses freestyle fighting.
It's evident that Ben is smart in some respects, possessing an above average intelligence.
Although he once again became cocky, he retained his selfless and heroic nature.
Ben has been trained in hand-to-hand combat by black belt Gwen, Max, as well as various years fighting aliens, and received a basic Plumber training.
It was even stated by Gwen that he really isn't working up to his potential at school. Physics and Chemistry are his toughest subjects, yet he still maintains a B average.
Ben has a good memory, as he was perfectly capable of remembering and writing down the mystic rune-like symbols for entering the inter-dimensional realm of Ledgerdomain with just one glance from a distance.
Professor Paradox has praised Ben's good nature, going so far as to say he had the gift to make the right choices at the right moments.